The invention relates to a brake cylinder for compressed air operated vehicle brakes, in particular for brakes of commercial vehicles.
In order to generate the large braking forces required, commercial vehicles are equipped with compressed air operated brakes. The “service brake” is operated in this case with compressed air cylinders, preferably in the form of diaphragm cylinders. By contrast, the parking brake cannot be operated with a compressed air cylinder, since the parking brakes may only act mechanically, as only in this way can a constant braking force be ensured for a virtually unlimited period of time. If parking brakes are charged with compressed air, the braking force could drop because of leakages.
For this reason, the brakes of commercial vehicles are equipped with “spring force accumulator cylinders”. The brake operating force is generated in this case via a stressed spring. This therefore satisfies the requirement of a mechanically acting parking brake. Since spring force accumulator cylinders generally provide very high forces, it is no longer possible for the brake to be released manually. Various solutions are provided in this respect. For example, the spring force accumulator cylinder is equipped with a release piston. It is possible with this piston, upon introduction of compressed air, to compress the spring to an extent such that the brake is released. Furthermore, it is also possible to release the parking brake by use of a spindle which is operated from the outside.
The parking brake is required only on one axle of a vehicle, this is the rear axle as a rule. Since installation space is limited, the brakes together with a parking brake are equipped with “combined cylinders”. A cylinder of this type consists in practice of two different types of cylinder, namely a spring force accumulator cylinder for the parking brake and a compressed air cylinder, preferably a diaphragm cylinder, for the service brake.
Nevertheless, a relatively large installation space is required even for this design. The commercial vehicles are frequently equipped with complicated chassis systems, such as, for example, individual wheel suspensions, lightweight axles and the like, as a result of which the installation space is limited.
In the manufacturing of commercial vehicles, it is therefore endeavored to find designs and ways of operation in order to minimize the installation spaces for the parking brake cylinder.
A “compact combined cylinder” has therefore been proposed, in which the function of the parking brake cylinder is integrated into the service brake cylinder. In this case, the spring force accumulator spring is no longer operated via a separate spring force accumulator piston but via the piston of the service brake cylinder. In order to release the parking brake, the service brake piston is charged by means of compressed air for a short period of time, but a special actuating means is required in this case.
The invention is based on the object of designing a brake cylinder for vehicle brakes of the type described above such that the required installation space for a vehicle brake of this type is minimized in a structurally simple manner.
The object set is achieved in that the spring force accumulator piston is arranged in the primary space which is to be pressurized for service brake operations. The brake cylinder according to the invention can therefore be considered to be extremely compact. In addition, the service brake piston is no longer loaded by the weight of the spring force accumulator spring.
The spring force accumulator piston and the service brake piston operate independently of each other such that the spring force accumulator spring can be released, for example, by a release spindle accessible from outside the brake cylinder.
Furthermore, another advantage is that the stressing of the service brake piston and of the service brake piston guide when subjected to a load, for example due to shaking, is reduced.
In a preferred refinement, the piston-resetting spring is arranged on that side of the service brake piston which faces away from the spring force accumulator.
In the release position of the brake, the spring force accumulator piston is at a small distance from the end wall having the compressed air connections. This distance is produced by the compressed spring force accumulator spring. In addition, the service brake piston bears against the spring force accumulator piston or is at a small distance therefrom.
If a braking operation is triggered, the service brake piston moves toward the opposite end wall, i.e. the distance between the spring force accumulator piston and the service brake piston is increased. If, however, the parking brake is operated, the pressure in the pressure space of the brake cylinder is reduced or completely dissipated such that the spring force accumulator spring can relax and set the brake. In this position, the spring force accumulator piston and the service brake piston again bear against each other. This way of operating the spring force accumulator piston and the service brake piston results in the compact design.
The spring force accumulator piston may differ in design. In a first embodiment, the annular flange of the spring force accumulator piston corresponds to the inside diameter of the brake cylinder housing. This simultaneously creates a guide by way of the wall of the brake cylinder housing. The service brake piston is charged either by a flexible compressed air line or by a centrally arranged ventilation pipe.
In order to pressurize the spring force accumulator piston, the circumferential surface of the annular flange thereof has an encircling seal. As a result, air cannot escape when the spring force accumulator piston is pressurized.
In a second embodiment, the outside diameter of the annular flange of the spring force accumulator piston is smaller than the inside diameter of the brake cylinder housing. When the parking brake is actuated, the spring force accumulator piston moves to the side opposite the compressed air connections and, in the process, carries along the service brake piston therewith. That region of the brake cylinder which is remote from the spring force accumulator piston is then vented. The ratio of the outside diameter of the annular flange of the spring force accumulator piston to the inside diameter of the brake cylinder housing is in the range of two to three.
Preferably, furthermore, that surface of the service brake piston which faces the spring force accumulator piston is of a stepped design. In this case, an outer annular surface protrudes in relation to the central surface.
Preferably, at least one seal, but more preferably two seals which are also separated from each other by a web, is or are inserted into the circumferential surface of the service brake piston.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.